NTSB Alerts Pilots on Weather Radar Display Problem

The safety alert issued on June 19 warns pilots using in-cockpit FIS-B and Satellite Weather display systems that the NEXRAD "age indicator" can be misleading.

The National Transportation Safety Board issued a safety alert on June 19 telling pilots using in-cockpit FIS-B and Satellite Weather display systems that the NEXRAD "age indicator" can be misleading. Actual NEXRAD data "can be as much as 20 minutes older than the age indication on the display in the cockpit. If misinterpreted, this difference in time can present potentially serious safety hazards to aircraft operating in the vicinity of fast-moving and quickly developing weather systems," the agency announced.

The alert says when a mosaic image created with data from multiple ground radar sites is updated, it may not contain new information from each of the sites. The "age-indicator" on the cockpit display indicates the time the mosaic image was created, not the time of the actual weather conditions. Thus, the NEXRAD image is always older than the actual weather conditions, NTSB said.

Its announcement says NTSB has cited two fatal weather-related aircraft accidents "in which NEXRAD images were displayed to the pilot that were presented as one minute old on the age-indicator but contained information that was up to five to eight minutes behind the real-time conditions." In extreme cases, the actual age of the oldest data in the mosaic can be 15 to 20 minutes older than the age indication the pilot sees, the alert states.

The two accidents were a March 25, 2010, Eurocopter AS350 helicopter crashing into terrain near Brownsville, Tennessee, and a Dec. 19, 2011, crash into terrain of a Piper PA-32 Cherokee small plane after in-flight breakup near Bryan, Texas.

The alert tells pilots that they should understand the common perception of a five-minute latency with radar data is not always correct, and it reminds them it is important to get a preflight weather briefing rather than relying entirely on in-cockpit weather capabilities.

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